Chemical process



Oct. 29, 1946.

D. L, CAMPBELL CHEMICAL PROCESS Filed June 13, 1942 l Il NW2 Oh.. "u 2h00 MN.. AV

Patented Oct. 29, A1946 CHEMICAL PROCESS Donald L. Campbell, Short Hills, N. J., assigner to Standard IOil Development Company, a corporation of Delaware Application June 13, 1942, Serial N0. 446,871

8 Claims. i

This invention pertains to the `production of `oleiins and diolens.

Most processes for dehydrogenation, whether by thermal cracking, `iixed bed catalytic cracking, `or Huid catalyst cracking operate to discharge products lfrom the `reactorata low total pressure,

'say .from Va pressure of `50 4mm. absolute to a pressure of l lbs. gauge. Whether the feed stock is butane to be dehydrogenated to butene, butene to be dehydrogenated to butadiene, or butane to be dehydrogenated to butadiene, the products include a large amount of gases lower boiling than C4. yThis means that it is impracticable to recover all the C4, including the desired butene or butadiene product in the liquid state by simply cooling the products or by a simple combination of compression and cooling even with injection of liquid from the lower pressure condensing stages tothe higher pressure condensing stages. Thus it is desirable to add an absorption system to compression in order to recover 'the full production of C4 cut.

It is an object of 'the present invention to provide a novel method of quenching reaction gases formed in any high 'temperature dehydrogenation, dehydrohalogenation 4or thermal cracking process and recovering a maximum of olens and diolens therefrom by a combined compression and/ or cooling and absorption system.

It is also an object of this invention to provide a novel method of stripping Wet "gas 'absorber oil in order that it may be reconditioned `for use in the absorption system and any C4 or C5 compounds containedtherein directly returned to the process.

It is a `iurther object of this invention to provide the lart with a novel .process of dehydrogenating AC4 and C5 compounds to olens and diolens and recycling unconverted compounds to the initial dehydrogenation step.

Other objects will appear from the detailed description andthe claims which follow.

.According to my invention, the hot reaction gases from a high temperature dehydrogenation or cracking process are quenched by direct contact with a fat oil whereupon the reaction gases are subjected to a compression and/cr cooling treatment in order to condense as much of the heavier constituents as lis possible. The uncondensed portion is then passed through an absorber wherein it is contacted with a suitable absorber oil which serves to withdraw the remainder of the desired C4 and higher compounds.

Ihegas passing out of the top of the absorber is released to the burner line. lThe fat oil witndrawn from the bottom of the absorber is released to a point previous to the rst stage of compression or cooling where it is contacted with the hot gaseous reactionproducts. This contacting at very low pressure and at as high an operating temperature as possible flashes the dissolved compounds from the fat oil and makes the resultant Ylean oil ysuitable Yfor re-use in the absorber.

Heat for the stripping of the absorbed constituents from the fat oil is furnished by the sensible heat in the reaction products. A further beneiit is obtained in that since vit is neces-- sary .to quench the gaseous reaction products, contacting the hot gaseous reaction products with fat oil serves the dual purpose of quenching the reaction products and stripping the fat oil.

rIhe vapors stripped from the pfat oil recycle through the compressors to the final stage where, due to the fact `that they are richer in higher boiling constituents than is the non-condensed gas ordinarily remaining after the last Vstage of compression and condensation, some of these ,recycled, absorbed, and .stripped vapors condense. The undesired llower .boiling constituents do not condense 'but go on to the absorber where vthey constitute a recycle `gas and eventually they leave the top of the absorber with the dry gas. .The increase in gas to be compressed and to be 'handled in the absorber is not substantial. i

My process is intended ,primarily to lbe used in connection with the production of butadiene from xed bed catalytic cracking of normal butenes. However, it could ralso be'used in connection with iixed bed catalytic cracking of butane or a mixture of C4 stocks to make butadiene or of butane to make butene, or of iiuid catalyst cracking with any of the above processes, or with thermal cracking with .any of `the above processes, or of thermal'cracking with 'steam with any of the above processes, or with high-temperature, low-pressure thermal cracking with or without steam, or of heavy naphtha or gas `oilto make butene, butadiene, or both.

The 'gure of the accompanying drawing illustrates diagrammatically a ow'plan of my process as applied to the production of `butadiene by the dehydrogenation of butene.

As shown in the drawing, I represents `a `source of supply of materials suitable for conversion to 'diolens, while 2 represents any suitable means for for-ming dioleiins at high temperatures, as by catalytic dehydrogenation, thermal cracking, dehydrohalo'gen'a'tion vand the like. Each Yof these processes is characterized by the formation of For illustrative purposes, the drawing shows an effective arrangement for catalytically'dehydrogenating butene to butadiene. rangement 3 represents a heater for preheating the butene to about 1200 F. or just below reaction temperature. 4 is a heater which serves to superheat the steam obtained from the live steam supply line 5 to a temperature suiiicient, upon admixing of the steam with the butene in suitableV proportions, to raise .the temperature thereof to reaction temperature. The steam may, for example, be under a pressure of 40 lbs/sq. in., at a temperature of 14:00c F. and admixed with butene in the ratio of 7 volumes per volume of butene.

Reactors 6 and 'I are provided, which contain a suitable catalyst. It is preferred that the catalyst by one having both dehydrogenation and Water gas activity. A suitable catalyst of this type is one containing magnesium, iron, potassium and copper oxides. Since a small amount of side reaction occurs unavoidably, there is some coke formation in the reactors. While most of the coke formed is converted almost immediately during the run of the reactor, due to the Water gas activity of the catalyst, it is preferable to shut olf the supply of butene to the reactor periodically while continuing the supply of steam, whereby any residue of coke in the reactor is converted to CO2 and H2. Accordingly, the reactors are generally arranged in pairs, so that one can function to dehydrogenate butene While the otheris subjected to a steaming operation to convert any coke present therein and revivify the catalyst. While the on-stream and steam--y ing periods may be varied somewhat, it has been found convenient when the reactors are arranged in pairs, to have the cycle consist of 1hour dehydrogenation time followed by l-hour steaming.

The butene-steam mixture is passed through the catalyst space at the rate of 500 volumes of butene (measured at standard conditions) per volume of catalyst per hour. The temperature at the inlet to the catalyst zone is approximately 1300 F. and the reaction mixture is discharged from the reactor at about 11'75" F. The butadiene is quite unstable at this temperature and, to prevent or minimize degradation thereof as by polymerization, it is essential to cool or quench the reaction mixture as rapidly as possible. Accordingly, the products leaving the dehydrogena-Y tion zone are quenched with a suitable cooling fluid supplied through line 52 which fluid may be water or fat oil hereinafter mentioned from absorber I6, and then passed through waste heat boiler 40 to the quench tower 9 wherein the reaction gases are cooled to from about 550 F to about 300?. i. e., a temperature sufciently low that the diolen is thermally stable but not low enough to condense the steam. A pump I0 is provided in line 3| for recirculating the quenching fluid through'the tower 9. A cooling coil or other heat removal facilities 8 may be provided in the line 3I to give the necessary temperature control in the quenching operation. The quenched gaseous reaction products are then passed In this ar- 4 through a cooler and condenser 53 to a separator I I wherein some of the water present is removed. The gases are then passed to compressors I2' wherein they are compressed to from about 1/2 to about 370 pounds per square inch gage. The compressed reaction products are then passed through Acooler and condenser 29wherein they are cooled to about 65 lkto'liquefyv the C4 hydrocarbons and then passed to a separator I3 wherein most of the remaining water is removed as the bottoms and the liquefied C4 fraction is vremoved through line I4 and passed to the stabilizer I5. The overhead from separator I3 is passed to the wet gas absorber I 6 wherein it is brought into contact with a suitable absorber oil such as light gas oil in order to recover essentially all ofthe uncondensed C4 hydrocarbons, particularly butadiene. Hydrogen, carbon dioxide, propanes and lighter hydrocarbon gases in dry form are discharged through outlet, I'I..

The absorber oil used in absorber I6 becomes more or less saturated with the Cs andhigher hydrocarbons contained in the gases passed therethrough and it becomes necessary periodically to subject the saturated or fat oil to a strip,

ping operation. VInstead of providing a separate.

stripper therefor, the fat oil may be stripped in an advantageous manner by passing it through line I8 to quench tower 9 where it serves as'Y the quenching uid. The fat oil may be, supplied to the quench tower atabout F., the temperature at which it, isidischarged vfrom the absorber, or if desired it may be subjected to suitable heat control before injection to assure proper quench-V ing in tower 9. If the temperature ofthe lfat oil is such that the quench tower Scannot take the full cooling effect of the fat oil, it may b passed in heat exchange relationwith the lean oil to effect temperaturey adjustment. v-The hot reaction gases strip the fat" oil, thereby directly returning the absorbed C4 hydrocarbons tofthe reaction products discharged from the tower` 9. The stripped or lean oil may be removed ,from the tower 9 and returned through line I9- tothe wet gas absorber I6 preferably after `passing through cooler 26 wherein the lean oilis vcooled to about 60 F. or sulciently low to assure efficient absorption of the C4 fraction inthe yabsorber I6. Auxiliary Ystripping means, not shown, mayalsobeused. a

The bulk of the oil in quench tower 9 is continue ously recirculated by means ofa pump I0. Due to a gradual accumulation of polymers inthe recirculated oil, it is necessary to bleed olf some of this oil to effect a separationof these polymers. Fresh make-up oil or the oil after the polymer separation is lsupplied to the system either through connection 5I at the quenching tower` or Vth'roug connection 54 at the wet gas absorber I6. The C4 fraction removed from separator I3 passes to the stabilizer I5wherein it is subjected to 'a fractional distillation to remove any gaseous impurities contained therein which pass as overhead to separator 20 and are discharged at- 2I`.V A liquid reflux may be returned from separator 2B tor the'still I5 through line 21. Thebottoms from still I5 are passed toa rerun tower 22`wheref in they are again subjected to fractional distillation. llf'he C4 cut passes as overhead'to separator 23, wherefrom a negligibleamount of Vgases are removed as overhead and the C4 fraction, containing essentially'butadiene, unconverted butene and some butane, is removed at 24Jand passed to a suitable extraction means 25 wherein 4butadiene is :separatedfrom the butene and .bu-

tane. The butene and butane separated in extractor 25 may be returned through line 30 to the feed, the reaction product may not contain any water, in which event water separation .in II and I3 would not be necessary unless, of course, water is used in the initial quench. When the reaction product is free from wateigitmay, if desired, be Ycooled sufficiently to liquefy the C4 and higher hydrocarbons without any danger of ice formation thereby obviatingthe necessity of compressing the reaction gases. In this case, the

reaction gases would be by-passed around theV separator II and compressor I2 and would go dir-ectly from the quench tower 9 through line 28 to the cooler or condenser '29 and thence to a separator I3 wherein the liquefied product would be separated from the Wet gases and passed to the stabilizer I while the wet gases are passed to the absorber IIS.

While the above description is for the most part directed to the production of butadiene, it is to be understood that my invention is not limited thereto but is applicable to the production of olens and dioleiins in general since, at most, only minor alterations in4 temperatures, pressure, and the like, from those disclosed above would be made when applying my process t0 the production of other compounds.

What I claim and desire to secure by Letters Patent is:

1. In the process of producing butadiene and homologues thereof wherein the diolefin is formed at relatively high temperatures, the improvement which comprises rapidly quenching the reaction products from the high temperature diolen formation step by contacting the hot reaction products rst with Water and then with a relatively cool liquid comprising a fat oil, separating cooled product gas from the quenching liquid, liquefying a diolen-containing fraction in the cooled product gas, separating uncondensed gases from this fraction, Washing said uncondensed gases with an absorber oil to recover diolens therefrom and utilizing the fat oil formed in this Washing step in the aforesaid quenching step.

2. In the process of producing butadiene and homologues thereof wherein the dioleiin is formed at relatively high temperatures, the imi provement which comprises rapidly quenching the reaction products from the high temperature dioleiin formation step to a temperature suiciently low to inhibit degradation of the diolens present by contacting the hot reaction products first with water and then with a relatively cool liquid comprising a fat oil, separating cooled product gas from the quenching liquid, liquefying a diolen-containing fraction in the cooled prod-V uct gas, separating uncondensed gases from this fraction, washing said uncondensed gases with an absorber oil to receover diolefins therefrom, utilizing the fat oil formed in this washing step in the aforesaid quenching step thereby stripping said fat oil of absorbed diolefins and returning the stripped oil to said washing step.

3. The-process of producing butadiene which comprises dehydrogenating butene to butadiene at elevated temperatures, rapidly quenching the reaction product from said dehydrogenating step i washing step in the aforesaid quenching' step 6 to a temperature suiciently low to inhibit Idegradation of the diolens presentby contacting the hot reaction products from vsaid dehydrogenation step first with water and then with arela- 1 tively cool liquid comprising `a fat oil, separating cooled product gas from the quenching liquid, liquef-ying a C4 fraction in said cooled product gas, separating uncondensed gases from said liqueed .C4 fraction, washing said uncondensed gases lwith an absorber oil .to recover diolefins therefrom, utilizing the fat `oil formed in this thereby stripping said fat oil of absorbed butadiene and butene, cooling .the stripped oil and returning it to said :washing step.

4. The process `of producing butadiene which comprises dehydrogenating butene to butadiene at elevated temperatures, rapidly quenching the reaction product from said dehydro-genating step to a temperature sufficiently low to inhibit degradation `of the diolens present by contacting the hot reaction products from said .dehydrogenation step first with water and then with a relatively cool liquid comprising a fat oil, separating cooled product gas from the quenching liquid,liquefy ing a C4 fraction in said cooled product gas, separating uncondensed gases from said liquefied C4 fraction, subjecting the liquefied C4 fraction to fractional distillation to separate gaseous impurities as well as C5 and higher molecular compounds from a fraction consisting essentially of butene and butadiene, washing said uncondensed gases with an absorber oil to recover diolens therefrom, utilizing the fat oil f ormed in this washing step in the aforesaid quenching step thereby stripping said fat oil of absorbed butadiene and butene, cooling thestripped oil and returning it to said washing step.

gas, separating uncondensed gases from said liquefied C4 fraction, subjecting the liquefiedyC4 fraction to fractional distillation to separate gaseous impurities as well as C5 and higher molecular compounds from a fraction consisting essentially of butene and butadiene, separating the butadiene from the butene in said product, recycling the butene to the dehydrogenation step,

'washing said uncondensed gases with an absorber oil to recover diolens therefrom, utilizing the fat oil formed in this washing step in the aforesaid quenching step thereby stripping said fat oil of absorbed butadiene and butene, cooling the stripped oil and returning it to said Washing step.

6. The process of producing butadiene which comprises dehydrogenating`butene to butadiene at elevated temperatures, rapidly quenching the reaction product from said dehydrogenating step to a temperature sufliciently low to inhibit degradation of the diolens present by contacting the hot reaction products from said dehydrogenation step first with water and then with a relatively cool liquid comprising a fat oil, separating cooled product gas from the quenching liquid,

liquefied C4 fraction, washing said -uncondensed Lgases'with an absorber oil to recover diolefms therefrom, utilizing the iat oil formed in this vWashing .step in the aforesaid quenching step. Y:thereby stripping said fat oil vof absorbed butadiene and butene, cooling the stripped oil, returning it to said washing step, withdrawing a part of the absorber oil from the system, separatingvthe polymers contained therein and returning the purified absorber oil to the system.

7. The process of producing butadiene ,which comprises vdehydrogenating butene to butadiene at elevated temperatures, partially quenching the freaction products from the dehydrogenation step by contacting the same with Water, contacting the partially quenched reaction products with Arelatively cool fat oil thereby stripping'the fat oil and cooling the product gases, separating cooled product gases from the stripped oil, liquefying a C4 fraction in said cooled product gases, separating uncondensed gases from 'said yliqueed C4 fraction, Washing said uncondensed gaseswith an absorber oil to recover butadiene and butene therefrom, using the fat oil obtained in this Washing step as the fat oil for contact with said partially: `quenched product gases thereby stripping said fat oiloflabsorbed buteneand butadienacooling the stripped absorber oiliand returning it to said Washing step. L

.8. In the process for the production of diele- Iinic hydrocarbons by a high temperature reac- .rtion, theimprovement Which comprises contactin-gfthehot gaseous reaction products rst with Water and then with a relatively cool liquid comprising a fat oil, separating the cooledgaseous reaction products from said oil, liquefying a frac- ,using the fat oil obtained in the Washing step as the fatoil for contacting said hot gaseous reaction products, vthereby stripping said fat oil Vof absorbed diolefmic compounds andreturning the stripped oil toj the Washing step. i Y

DONALD L. CAMPBELLL 

